Can't compare them, totally different rackets. The Power 7 belongs to the Power series line. It's essentially identical to the Power 10, except a little more flexible.
The Power series rackets were designed to offer power without sacrificing too much control, while maintaining player's racket specs as far as a weight and stability.
The Power 7 is a very crisp racket bordering on HYPER crisp, I'm not sure, no I KNOW I've never tried any rackets as crisp in their shot response as the Power 7 and 10.
The Power 7's got a bubble gum wrapper type crispness to it, a candied-like shot response, crisp, sweet, pure in a sugary, crisp, fresh donut, glazed sort of way.
It's got POP, yet still has a bit of butteriness to it. The spin is sensational, it's got MORE spin than the RD-7, the string pattern is noticeably more open.
It's basically like taking the classic wholesome, signature, oatmeal, sogginess, of the RD-7 and surgicially injecting a mechanical spine into it. The RD-Power 7 is a feat of Japanese robot, engineering, comes in Transformer bubble gum blue but lacks a soul.
With that said, it's also a very unweildy racket, redundantly stable and solid but unwieldy due to the weight of the racket and lack of an aerodyanmic body.
It also lacks the OPS, oval pressed shaft feature which to me does make a difference. OPS rackets have that unique feeling of flexing at the shaft that non-OPS Yonex rackets don't have, even gastronomically flexible ones such as the Power 6.
It does, however, have vacuum pressure molding, which also does make a difference. Vacuum pressure molded rackets have a cleaner, purer shot response to them, less muddied, it's basically like comparing pure filtered water vs. water full of sediments taken straight from the stream complete with little pebbles and earth worms.
The RD-7 has an oatmeal, old soul feel. It's more wholesome, has a more controlled, tighter spin, a little deader, a little boring, but old faithful, loyal, and reliable. The Power 7 lacks that soul you can't quantify, but it does however have admirable qualities all its own. It's what a Babolat Pure Drive Plus wishes it could be...only without the mobility of the Pure Drive Plus. If you can get it in an L1 grip size, which is significantly more mobile than even the L2, then L3 and ups, then you'll have a superior Pure Drive Plus with better control and a much purer feel.
It'll turn you into a modern-day samurai warrior slightly assisted with the wonders of modern technology. Aided by modern-technology, yet also just transparent enough so that you aren't MADE by the technology, a product of the technology.
Power 7 is heavier, both are pretty flexible. I wouldn't describe them as completely different rackets, but it is possible to like one and not the other. The Power 7 Long really lacks manueverability, as it is Long AND Heavy.