Couple of sidemount questions

My current certification is Advanced Nitrox/Deco Procedures and I'm looking at taking the two trimix's next year. My goal is to make a dive late next year to a site in open water in about 300 feet. My current setup is a Knighthawk bcd and I own two Hp 130's and one has an H-valve. I also own a 30ft3 pony and dive dry primarily. I want to move into sidemount for several reasons and I need some advice on which system to get. My LDS sells the Hollis 100 and the OMS system so I'm leaning towards one of them. The last time I talked to my LDS they were suggesting the OMS over the Hollis but I don't remember why (that was a while back). What would be the cost difference since I don't have a BP/W to add just the OMS adapter? I want to use the tanks I have now, so how much lift would I need for those big tanks? Also, I will be having to purchase bigger stage tanks for the deep dive once I get to that level, so how much would that change your answer on lift? As I have not taken the courses yet, would sidemount offer enough room for dives that deep, or would I have to backmount doubles and sidemount stages? Take it easy on me as I plan to follow the proper avenues such as talking to different instructors and taking a course, I just want a little information beforehand to do some initial planning. And I'm sure some eyebrows will be raised concerning me wanting to use the big tanks. I'm 6'2 230lbs so I've got some room for them. Also I've got a lot of money to spend on new gear and I'd rather not replace something that I absolutely didn't have to. Thanks in advance.

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---------- Post added November 9th, 2013 at 09:03 AM ----------

Also, as DEMA just happened, should I hold off a little bit to see what's around the corner or would I be happy with one of those two?

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There are a lot of different sidemount systems available and which one works for you is a personal decision. My suggestion is to try several different rigs before spending the several hundred dollars on one. Find a SM instructor who has several rigs for you to try. Personally, I own over 1/2 dozen different models. The HP 130s are heavy tanks so you will need some decent lift with that but most of the rigs offer 50-60 lbs of lift and will work. I would advise against using the OMS adapter. While it might work it won't be optimal. HP130s will work fine for deep dives. That's plenty of gas. I recommend taking the tanks you're comfortable with at that point. If you're still building muscle memory in sidemount then go backmount. If you've done a bunch of sidemount dives at that point and have the muscle memory and comfort then go sidemount. It also depends on the site and what the needs are. Sidemount is a great configuration but it's not right for every site.

For your complete options, do see: A List of Modern Sidemount Diving Systems

I am a huge fan of the Sms100... you will need to make some mods unless your using steel tanks. But if your looking for something that will meet the needs of diving to 65'-100m' in sidemount config. I think its your best bet...