Marathon fuelling advice

Hi folks,

A quick bit of fuelling advice needed. I was using solely jellies on my runs to date - a combination of Clif Bloks and PowerBar Powergel shots. It had being going well.

I found yesterday on a long (27km) run towards the end that my stomach just started to disagree with them. Maybe it was the last 3 that I took which were the caffeine Clif Bloks, but my stomach felt like it just shut up shop at that stage.

I had taken 3 x non-caffiene Clif Bloks, a packet of PowerBar Powergel Shots, and 3 x caffienated Clif Bloks.

I've got 4 long runs before the marathon itself, so I'm looking for advice. I'm gearing towards PF90 or Maurten Gel Mix 480, but the latter would be a bit of a change to carry a larger bottle with this mixture.

How do people find the PF90, or what else do people do? My key things I want to do is to avoid carrying a running vest/belt (I have two thigh pockets and a rear pocket in my shorts) and I want it to be mixable on the fly - either into a bottle or with water.

I have also used a Maurten Solid C160 bar which agrees with me very well, but its a lot of bulk and I think chewing them could become effort in the latter stages.

Welcome peoples thoughts and opinions, obviously this is a "what works for you might not work for me" style question but I'm open to ideas.

Thanks!