basic strategy is clear, you should surrender a total of less than 17 against 8, 9, 10, A if you cannot hit again. The only interesting card is the 7. is there a bust propability of less than 25% at high counts? or is the count so high that it is not interesting? the normal bust propability of a 7 is about 26%, so it may be a closed decision at high counts, especially interesting if you want to avoid variance.