[ThiloHarich]

If I use a Factor Base size of 1624 I have the following timings:

Time sieving 2.014 sec
Time factoring .406 sec
# polynoms: 792

If I use my Factor base with size 4022

Time sieving .922 sec
Time factoring .535 sec
# polynoms: 331

Search Interval is 157228, I use no large Primes here. I do not know how to speed up sieving, since it is just a simple loop.

while (xIndex < length)
{
qLength [xIndex] -= factorLength;
xIndex += factor;
}

For the large Factorbase switching the polynomial needs only a small portion of the running time.