Light rubber = soft sponge. You're used to harder sponge. So it won't play the same at all. The difference will probably be a lot bigger than 'just lighter and possibly faster'.
Also Rakza X is very fast. You want faster?
Some light rubbers I adore are AK47 series (the softer, the lighter, usually) which come at like $10 a pop. Not as fast or grippy as Rakza X, you need to really learn how to use the sponge rather than just the topsheet to get the full effect, but it's a grand full effect.
An AK47 rubber cut to the blade can weigh like 38 grams, which is insane. But there's some variation in weight since the sponge hardness have a certain random range. For example, AK47 Yellow can be from 42 to 44 hardness.
I experimented until I find a setup I really like, which is Liu Shiwen ZLF with AK47s, weighing a total of 160 grams despite the LSW having an oversized head. I think that is easily 30 grams (or more) lower than most 'regular' setups.
Some good ones are the new omega euros which have a grippier topsheet but cost more like $60 a pop or something
And there's everything in between.
Maybe older omegas, like omega 4s? Or Rakza soft? Though I dunno how much those weigh.