Also seconding the 14-28. Much less fuss than the 14-34 which needs MTB derailers and has a huge jump. I don't particularly have an opinion about 6 vs 7 speed, but the 6 is 14, 16, 18, 21, 24, 28. The 7 is 14, 16, 18, 20, 22, 24, 28. The 39t will help, but it may not shift well without a ramped and paired 53t chainring, although people have done crazier jumps with half-step and granny setups.