You can use math to figure out the rate.
The normal 1/512 rate at 50% boost would be calculated as so:
r = 1 / 512;
r *= 100 + rate_boost; // in this case, rate_boost is 50 and at this point, r = 0.29296875
r = 100 / r; // r = 341.33333(repeating)
r = round(r) // r = 341
r then becomes the denominator for the new rate. So, in this example, the final rate is 1/341.
If you do the same math using r = 1 / 10 (at the top for Kondrieu), the final rate becomes 1/7. (Because r ends up rounded from 6.66666blahblah7 to become 7.)