If you decide to go the swap direction, likely a JDM V7 or earlier with the 6MT would be your best approach. Stay away from the USDM STI swap as itís simply not worth the overwhelming cost. Youíll spend upwards of 10k for an sti swap.
Or another option since youíre already part way there with your hybrid model, you could always do a hybrid wrx/sti swap. Itís a direction Iíd like to go with my setup someday. Basically gives you the largest bang for the buck. Go with wrx heads, ecu, and wiring with either a ej207 or ej257 shortblock. This will give you sti power with the ease of a wrx style of swap.
For the transmission, yes the sti 6-speed is the best factory tranny available but it costs an arm and leg. Not to mention youíll either need to re-gear (ring and pinion) your rear diff, or run an sti rear diff, shafts, subframe, etc. all of which adds to the price. Another alternative is beefing up the wrx 5MT. You go with the modest sti-ra gears and new clutch for 3k (as opposed to the sti 6k+) and hold 350hp, or go with a more solid PPG strait-cut 1-4 and new clutch for 4k and hold 450hp+.
Look into the costs of the 6-speed swap. When you get disgusted at the crazy prices for the trannyís consider gearing up the 5MT. Also, Iíve seen you can buy an entire 5MT dogbox new for the same price as the sti 6-speed.
Okay, thatís my $.02Ö