I had a 92 TC with the 4.9, and put over 200,000 with little problem. low end power was great, never burned oil but ran out of breath around 4000 rpm. overall a much better engine than the old 4.1. the oil pressure was greater, and that helped the lifespan.
I now drive a 97 Eld with the 4.6. overall, much smoother, and fast as hell over 25 mph. Have had some complaints...weird 2 peice block tends to leak alittle oil. Expensive to maintain..it takes 7.5 qts of oil. however, it loves to rev, and it is one of the smoothests V8 's ive ever owned (i had a few hot 350 chevys in my day).
both are fairly good powerplants..i favor the 4.6 for power and economy. I can get 29 mpg on the highway cruising at 75 all day. not bad for a bigger casr with 275 hp!