Skateboard size help.?

iv been skating for a year and a half now. and i always been confused about what skateboard size i should get. i wear shoe size 10 to 10-5. 170 pounds and 5"7. this is how my little story is. ever sinced i started skateboarding i started with an 8. the only problem is my ollies. i can 3 flip with 8's pretty good but when i ollie its an entire different story. i set my feet in kick flip position to ollie. if i put my feet up more it doesnt feet right so i dont ollie as good. so i tryed getting a 7.75, all my flat ground tricks were good and i ollied very good. but the problem was with the 7.75 was i couldent land stair sets or gaps. it felt like the board wasent under my feet with the 7.75. stairs and gaps are a big deal in skateboarding for me. so the question is what size should i get so i can do big gaps and stairs. also when i do stairs and gaps with an 8" my tail of the board kinda turns a little which is also something im doing to avoid. any help?