Just upgraded my speakers - do I still need the subs

Yes, there is no way a 6.5" driver can produce real low bass even with the help of a port (I don’t like ports). Lack of low bass, makes this speaker size sound very clean, impressive, some makers like KEF do an amazing job at that, but ....

Keep the subs, and get thee a SPL Meter, inexpensive ones work well to blend the Sub with the KEFs.

This one has a tripod mount on the bottom, so you can position it on a tripod at seated ear level, and get hands free vibration free readings.

https://www.amazon.com/Digital-Decibels-Battery-Indicators-Factories/dp/B0DQKP4LDV?psc=1&ref_=sspa_dk_detail_gen_ai_1&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM=

I use this test disk with 29 test tone frequencies, tracks 9-38

https://www.discogs.com/release/7290000-Various-Amazing-Bytes

Expensive, I bet I could help you find an inexpensive copy, I keep asking for suggestions of test disks from members here, no one suggested anything yet. Use a CD, not an LP.

Using the SPL, make sure your system is balanced L/R before you set them up with the subs. My friend is having a devil of a time with a weak right side, using his preamp’s balance control to listen now, but....

You can download test tones here Source: Hsu Research https://share.google/et8a6EKJnUpEbnrRL

A/B test.  Listen to music you know by heart that has a lot of low bass or organ with the subs.  And then without the subs.  Do you notice a difference?  You should if the sub crossover settings are correct for your subs and speakers.  The subs not only deliver more low Hz output but they also allow your speakers to focus on producing mids and highs.  If not consider upgrading your subs to match the excellent speakers you just purchased.  A lot of great choices available. 

By all means keep the subs. I've R7 Metas with a pair of those same subs you have and they add a new dimension to those KEF's in a very seamless way.  You don't hear them until you take them out.  I had LS50's before, albeit without the subs.  I wouldn't sell the subs unless you just need the money.  They are very good and very unobtrusive. 

The -3db at 45hz rating is taken at about 10 inches away from the speaker at very low volume, and is essentially non existent at the listening chair...I believe a pair of subs can help any speakers...