I can't speak to SS+ because i don't use it myself, but i can tell you as far as vanilla ships go burn speed isn't limited by the ship nearly*1 all destroyers are burn speed 4, and cruisers and capitals hover at burn speed 3. As i recently said in another post if your main concern is speed for catching up to AI fleets i'd suggest heavily investing in the navigation skill, this provides a small bonus to cruisers and caps and a moderate bonus to destroyers.
However if you're going primarily for combat skills IE you prefer to have one ship rather than a fleet, then putting just a few points into tech and grabbing the Augmented engines hullmod is the way to go. it is similar to unstable injector but it costs a bit more, doesn't cripple your ship as badly when your engines take some fire, and it gives you 2 burn speed rather than 1. You can also grab a single tug if that is more your style, as it is a frigate it's quite fast so the thing it is helping to carry will always be the one slowing down the fleet not itself. If you're going for the solo combat ship style then it's the only way to use bigger ships because you want all the extra OP's you can save for bigger guns/more vents/caps
Another thing to keep in mind in general is destroyers in a frigate heavy fleet engagement are primarily meant as the ship the battle will take place around, yes they'll maim and destroy any frigate stupid enough to close in alone, but smart frigate commanders will just leave them alone because no destroyer, can catch up to frigates. In other words you only need a destroyer if you have an enemy destroyer or cruiser on the field. If you're still fighting frigate fleets and the occasional buffalo MKII and you really want a destroyer, get a carrier, having fighters as an option in battles will drastically reduce your losses and annoy the heck out of the enemy, nobody likes dealing with fighters they are pesky, tiny, full of guns and won't stay dead.
I personally love the hammerhead, slap an ITU on it and range isn't an issue*2, even with assault guns. Or give it one mauler and one HVD and you've got the makings of a ship that will kill just about anything that is in it's own weight class.
The Medusa the most popular vanilla destroyer it is obviously nearly impossible to hit with missiles because it has full 360° PD coverage ( if you actually put PD in those small slots) couple that with it's speed, maneuverability, skimming and two medium main guns and it's a force to be reckoned with.
The Sunder is an oddball it hits far above it's weight class, but can't take much of a hit itself. if going up against small ships you can give it a tachyon lance and basically no frigate will ever survive the encounter. ( assuming you can lead your targets) give it a plasma cannon and you can kiss your enemies goodbye regardless of their weight class, a single volley is usually enough to kill frigates.
My personal favorite is the Enforcer, a low tech brute the idea behind it is fill it with guns and reapers, and then bum rush your opponents. The most straightforward destroyer of them all in my opinion and it's burn drive makes it surprisingly quick on the battlefield.
The Mule is an interesting ship it is essentially half of a Venture cruiser, as such it it way more durable than you might think, and is capable of holding it's own against other destroyers simply because of it's refusal to die.
last of the actual combat destroyers the Buffalo MK II is another glass cannon like the sunder however with no shield it is even more so. if outfitted properly these rusty old boats are actually incredibly dangerous their lack of shield is compensated for with more guns and missiles than any other destroyers, and with the changes to missiles recently it's wealth of missile slots makes it absolutely deadly. due to their commonality a useful thing to do with them is fill them with reapers, dump them all into a capital ship and then either retreat or suicide run into it. ( to be fair bringing one of these near a capital ship is already mostly suicide)
Gemini and Condor, i group these two together because they are carriers, and as such you'd likely never fly them yourself. the better of the two is the gemini, it can mount up two medium ballistics and a medium missile for support whereas the condor can only manage small ballistics and one medium missile. however the condor does have the fast missile racks mod so if you want fighters but also want a lot of missile support going with condor's isn't a bad idea.
The Tarsus, Buffalo, Phaeton, and Valkyrie are all freighters of their respective /cargo/fuel/people, if you're flying them something has gone terribly wrong. Although they definitely serve their purpose in fleets that actually need them.
*1: defunct or defective destroyers are always lower than 4.
*2 technically range is limited by the weapon very rarely that range is affected by the layout or size of the ship, only capitals really suffer from this, and the ITU will fix it regardless of where the problem shows it's face. If you think a weapon is too short range then upgrade, get a bigger gun, even in the same slot size there are a lot of better weapons out there, if you're using standard PD lasers, then yes they are very short range, either try out the LR PD laser or slap the advanced optics and ITU on it then watch as your PD lasers go extremely far.
