Isn't man spider really stupid though? I mean if your talking about the Man-spider I'm thinking about (the one in the Cartoon series in which Spidy morphs into a big...well man spider). If he is stupid Venom would rip him to shreds.
I don't think Man Spider would be stronger than Venom and if he was it wouldn't be by much. Next Man Spiders only real attack would be to hit Venom since Venom's Symbiote would protect Brock from slash attacks and stuff, and Physical attacks of any kind, not including high heat or Sound, may knock Venom around and slow him down but they really don't seem to hurt him. Finally Venom may not be as science smart as Spidy, but remember Brock was a top student and athleat in school so he's no dummy, and if you ask me he is smarter street smart wise, and just instictivley survival wise than Spidy so Venom would have the brains to defeat Man-Spider.