The extra lead will raise the wingloading but it will still fly fine. Did you mount the servo's in the tail? That and moving the battery back might balance it without so much weight. Your 90 should be fine just don't use much pitch on the prop to help keep the speed down. I have flown mine a few times with a 13x8 on my 91 FS, coming down from a split s with the power on really makes it whistle.