1) In our company for calculating the IRR we often use the European version with act/360 instead of the act/365 that is used in the XIRR. Is there any chance, that the formula XIRR could be extended so that you could choose the exponent you need (similar to e.g. the COUPDAYS funtion, wehre you can choose the day count basis) or if there is the possibility for a new function XIRR360.
2) I have tried to calculate the IRR with the net present value formula stated in the XIRR support page. However, when I than search for the IRR with the excel solver, the IRR is slightly different from the one, that XIRR gives me. This can't be due to the iterative technique, because even when I give my expected IRR as an "Guess" to the XIRR formula, it still gives me a different IRR. How is this possible?