I've been out as often as possible in my newly acquired Zodiac Pro 420/Suzi 25 the last few weeks but this weekend the forecast was F5 gusting F6 for Southampton, so I chickened out!
I have the same boat as you, but with a bigger engine and an auxilliary back-up. I've experienced conditions on the west coast of Lewis with a north-westerly blowing F5/6 and a F5/6 in the Moray Firth.
My recommendation is always to stay within a limit you feel comfortable in. Remember weather conditions can change quite quickly. Add in squally showers, an engine that's not behaving properly, and what started as a F5/6 can feel much worse.
The Zodiac Pro has a relatively shallow V and tends to 'slap' on-coming waves rather than cutting through them. It'll handle it okay, but you or your passengers will spend a degree of time airbourne as you negotiate the swell.
Better to call off, rather than press ahead just because you've prepared to go out. It's a pain when the weather is poor, but sometimes you just need to wait for a window. Personally I'd only go out in a F5/6 with someone else on board. Basically to keep the bow down!!!