With v14.3, I'm getting 2.5gps (GRIN31) poolside using two 1080 Tis at +180/+600/85% on F2pool with 1.2% rejected  I found in the past that both sparkpool and grinmint had too high rejected shares, so haven't bothered with them. I did have pretty good luck with Luxor on Grin29 - near 0% rejects, which makes sense because my ping is ~55ms at Luxor compared to ~330ms on F2pool. I'm planning to go back to Luxor after my next F2pool payout.