Just my two cents.
Be careful going for a high speed setup. It can be very costly, and that's not even towards the end. Just as a personal reference, I thought that you could introduce a high speed motor into a stock gun. Do not do this. You'll hate yourself for it. I'm not sure if high torque requires the same things yet, haven't delved into it very far yet, but high speed requires that you basically revamp your gearbox.
One of the first things I noticed that needed to be replaced was the shims. Unless of course you have metal shims already, I wouldn't be too worried. One of the things with a high speed that I'm aware of, is that you need a reinforced mechbox, preferably 7mm, or 8mm. Reason being that because your ROF is so much higher, your gearbox is functioning that much faster, and you could potentially crack your gearbox, and obviously that's a boo-boo. I could be wrong on this one, but you also need to upgrade your bushings to solid bushing fo the appropriate mm (7mm solid bushing if you havea 7mm reinforced gearbox, etc). Bearing bushings are apparently bad idea, I'd need confirmation on that though.
You'll also need to replace your cylinder and piston. A smoother cylinder results in less friction with your piston, which results in less heat, which results in less problems. From what I know, stock cylinders are not the best things you could have. A new piston is a must. I saw an example of someone who used a high speed motor without changing to full-metal teeth, and the teeth on his stock piston were chewed to pieces. All your other lovely parts also must be replaced with metal parts, if you haven't already. This means your spring guide, cylinder head, and air nozzle. You may also need to downgrade your spring. My personal opinion would be to go for a S100/M100 spring. You can't go above that, I'm not sure what the direct consequence is of going above that, maybe someone else can fill you in on it, but just don't do it. Going to a S90 or M90 may benefit you more, not sure though. You'll also need a new tappet plate, especially if yours in just a stock plastic one. Even if it's a stock metal one, I'd recommend upgrading it just in case. I'd also recommend a sorbo pad. Your gearbox won't suffer as much of a beating with one. You'll also need high speed gears, obviously. Stock gears just won't cut it. I'm surprised I didn't shred my gears when I put my high speed motor in.
Like I said, I'm not sure if high-torque is this high maintenance early on, but high speed, from what I understand, will require you to upgrade everything accordingly before you can even think about fielding it. Also, high speed = less accuracy. So unless you play indoors all the time, I'd suggest not going high speed. You'll just end up going through an entire mag trying to get a hit on someone, and then maybe not even hitting them. Just for the love of God, if you are going to go high speed, make sure you're completely fitted for it, and not half-way upgraded. I'd hate to see you come back asking how to fix something resulting from not being properly upgraded
