Well, I think if you skip the tomb on korriban (or can't enter due to being too neutral and also never get your prestige for that matter--like I did my first game ever in TSL), you only get something like level 26 or thereabouts.
Otherwise I just go flat out to the full 50. More feats and powers to play with. Except for some odd reason the whole immortality at 0 health in the tomb area with the unlimited exp loop stopped working once I put a simple mod in it. I myself actually think it has something to do with the inconsistencies of operating it with the patch on Vista, relating somewhat to TSL being one buggy mo-fo.
TBH, though, I'm not really sure why they'd make a Lv. 50 when in the game you can barely achieve half of that naturally.
Also, don't get caught without a prestige class, it sucks.
If you do consular or its natural progression and have not solidified your physical combat progression very well, Sion is VERY HARD.