the large turbo model is more sought after as the managment system it has on it is much easier to tune than the st model, iirc the st model is costly and difficult to get over 300bhp tho what it lacks in lag with the tiny t25 turbo makes up for instant power at any rpm.
also one thing to check for now as these are starting to get on a bit is rot, some are starting to rot quite badly these days as not all of them are as cherished as we would think
obviously you get what you pay for 13k should grab you a tidy example but i wouldnt personally expect anything mint or highly/well tuned for that money