I don't have solid proof this is always true but I seem to have had the best luck on large shift block hits when mining solo at night (during night time the large firepower pool miners don't mine as hard making the rounds longer though I've gotten large shift records on both solo and pool).  

All you do is append --shift (bigger number than default 25).  Example: ./gapminer-cpu -o mine3.gap.nonce-pool.com -p 3385 -u -x --stratum -t 16 --shift 256.  The default sieve and sieve primes have worked fine for me when being speculative with large shifts.  A shift of 256 has gotten me into the 8000-9998 list several times.  Did some calculations and shift 380 & 381 got into the 10000-14998 range which if you solve any block with difficulty 22-23 you have a very good probability of a world record every time with where the records are.  Keep in mind, these higher shifts will severely punish your pps rate since you're looking for larger overall gaps AND all the numbers you're testing are bigger: shift 25 are 85 digit numbers vs shift 256 are 155 digit numbers.....which is why solo mining probably gives you better odds (with a solo target you're putting all your chips in the middle to solve the block, not accumulate shares/coins).

If nscythe or skif (the two powerhouse pool miners) are reading this, they could probably set a couple hundred new world records within a week with these higher shifts if they really wanted to.  Gapcoin taking over more of the record lists I would think could only help it.

EDIT: Just set another record a few minutes ago with length @ 11202 (on block #109634). You can see it was set with shift 391 from the block record -- https://bchain.info/GAP/block/9248f5e0765cd8618f55aea2c3c46270b0304eb14be32a6ae879d9198134cfb9