Since you have the smaller saw for limbing, I would then definitely recommend the 7900. I love it.
The filter issue is not access, that is great. Couple spring clips, a retainer, and it is off. Probably the fastest of any saw I have or have used.
The air filter problem is well known and discussed, but certainly not crisis or show stopper or saw damaging. I would not shy away from the saw because of it, but do be aware of it. I am hoping the upgrade kit (to be offered as aftermarket, but not incorporated as standard production line build from what I have heard) resolves all of the issues.
Several issues : air flow to the element, air bypassing the element at the joint, and air flow through the element media itself.
First, air flow to the element. The housing holes at the front wall are somewhat restrictive compared to the engine size. The new housing (I've heard about $10) has holes and screen all across the divider wall, not just a few holes on one end. That is an attempt to address the air flow to the element, as well as presecreen out junk which is item 2.
Second half, element efficiency. Two complaints seem common: bypassing around the filter mounting joint, and material passing through the media. I have seen both. The joint is easy to fix with light silicone dielectric grease. Not a good choice for woods work that may require cleaning filter mid day, but works ok for me.
Like any engineering decision, there are tradeoffs to reduce weight and size. One of Dolmar’s attractive features is the weight and size for the engine size and power. They had to reduce every single item by fractions of ounces to add up to a couple pounds of weight savings. I am very glad they did, I love the saws light weight, but those tradeoffs have costs.
For any filter, pressure drop goes up as filtering efficiency goes up. Smaller pores or less surface area = more restriction. Larger area, or larger pores = less pressure drop, less efficiency. The element is neat design with many pleats and folds to get a lot of surface area in a small volume of space. It must have been not quite enough as Dolmar seems to have opted to a fairly large pore media. One complaint is that fine dust (wildfire use for instance) goes through the media and shows up in carb and throat. Wildfire use doesn’t apply to me, but even in homeowner use I have seen some dust through the media. Not unusual, but noticeable. What I have noticed a lot is that sliver shaped wood particles work through the media and end up either trapped in the v folded ends of the media (which is fine) or probably pass right through into the engine. (no, wood is not harmless to the engine. No particles are.) I design hydraulic systems and work with filters a lot. My .02 opinion is that the air velocity is too high, the pores are too large, and the air moves the dirt through the elements. This shows up in a couple hours of use. Hopefully the filter upgrade kit adds enough area to slow down the air velocity, and tightens up on the media layers to reduce the dirt.
Many don’t have the dirt issues. Even some millers have good reports of the filters, so they certainly are not a crisis for Dolmar. But I do believe it is an issue. If I were a pro cutter, maybe different story, but as a homeowner/firewood cutter, even with the dirt that I see in two hours, the saw will likely last me the rest of my lifetime with no more overhauls. I say go for the 7900, I think you will like it a lot.
kcj