I agree with Gary that each trail system has unique challenges. However, I did 35 miles at Croom on 12/20 after two weeks of no riding and battling the flu. It took me just over 4 hours and I had over 2600 ft uphill. I then rode 25 miles (one lap of the wt50) on 1/1 and it took me 2.5 hrs with only 1100 ft of uphill.
Doing 50 at WT will be just under 6 hrs and only 2200 ft of climbing. Yes there are more challenging roots and pig holes to keep you on your toes, but as far as climbing, there is very little at WT then at Croom. There is also less sand at WT. So I would say for me, it is as much effort to do 35 at Croom then doing 50 at WT. (that is 35 at Croom!) I will even say 35 at Croom is also close to doing the Santos Epic. Croom 50 would require way more effort of me then the Santos Epic+ (50). Oh, I did do all the hard options at Croom.