Reverse ink & grading

What is the highest grade one could expect from SGC on a card that has an ink stamp on the reverse? Their grading scale allows 'ink and pencil markings' up to 30/2, but I'm pretty sure I've read & seen around that cards are often given 20's regardless. Right or wrong? The card in question is in a PSA 4 (mk) slab now and I'd prefer to cross it...knowing the grade will suffer for sure, but...how much?

Edited to add: If anyone has an example of a card w/ stamp that has been graded above Fair, I'd love to see.

imo you're getting a 20 ray. good part about the sgc20 is even if the card would've been a psa2mk, it's going in as a 20 too. i don't think i'd cross a psa4mk, but you probably want uniformity within your set.

Thanks, Quan. Pretty much what I was expecting to hear, and pretty much what I was expecting when I bought the card. I might hold back on this one for now, though. It'll eventually have to cross if I'm going to keep it long term, but it feels like too big a bullet to bite at the moment. Blech.

BTW, if anyone needs to cross cards and hasn't yet seen, SGC is having specials this month.

Ray, crossover with SGC is nicely handled, you can state a minimum grade you will accept on their service form. If they are unable to accomodate you they will leave it in the original holder and return it.
If you do take advantage of the special this month please post how it went. I have three PSA 4(mk) w514's I'd like to crossover. Thanks.

I agree with the above, except that Ray didn't specify if it was a factory stamp or not. If it was a factory stamp, SGC will now grade it without a deduction for the stamp, but will note on the flip that it has a factory stamp.