RSA key size restriction?

[Ludwig Hügelschäfer]

Hello,

 > Why is the RSA support in GnuPG limited keysizes <= 4096 bits?

I think, one should limit the size to reasonable sizes. It is said, that 
the computing effort one needs to factorize an RSA-key with 3100 bits is 
about the same as to break the session key per brute force. AFAIK the 
amount rises with the square root of the exponent of the bit count. So 
the amount for a 4096 bit key should be sqrt(2^4096/2^3100) = 8,2e+149 
as high... I don't see any reason for larger keys.

Ludwig