I have some experience to share with the board members. I've crossed-over 30 1952 Topps Wings cards to SGC holders and cracked-out 24 of the same cards to submit to SGC as raw cards. In my humble opinion, SGC is a little more unforgiving with regard to corners and tilted prints as is PSA. Here's my approach: when I receive a PSA graded card, I try to determine if it will cross at the same, or higher grade. This is totally based on my experience in submitting over 300 cards to SGC. If the card looks O.K., I send it in as a crossover. Sometimes I feel I can enhance the card somewhat by a little judicious fiddling. These cards I crack out and submit as raw cards. I have had a few PSA cards that I would not submit to SGC because I just knew that they wouldn't cross successfully. Most of the cards listed below were submitted to SGC before PSA went to half-grades, so that sometimes I could gain a half point for "free".
Crossovers: 3 PSA 9s yielded 2 SGC 96s and 1 SGC 92.
2 PSA 8.5s yielded 1 SGC 92 and 1 SGC 88.
22 PSA 8s yielded 1 SGC 96, 1 SGC 92, 17 SGC 88s, and 3 SGC 86s.
3 PSA 7s yielded 2 SGC 86s and 1 SGC 84.
Crackouts: 10 PSA 8s yielded 2 SGC 92s, 5 SGC 88s, and 3 SGC 86s.
11 PSA 7s yielded 5 SGC 88s, 4 SGC 86s, and 2 SGC 84s.
2 PSA 6s yielded 1 SGC 88 and 1 SGC 84.
While this data isn't earth shaking, it does show that SGC is a little tougher on crossovers, and that some advantage can be gained with "enhanced" crackouts. You can see from the data that I've had the most success cracking out PSA 6s and 7s. I'm still and SGC guy. I think the Wings cards look awsome in SGC holders. I've had a lot of positive experiences dealing with the SGC customer service team.