Yes, if push up to RM1.5K, there will be plenty to choose from:

1. Huawei Honor 7 (RM1399)
2. Samsung Galaxy S5 (RM1499)
3. Sony Xperia Z2 (RM1399)
4. Oneplus One (64GB) (RM1250)
5. Samsung Galaxy Note 3 (RM1599)
6. Huawei Honor 6 Plus (RM1399)
7. Xiaomi Mi Note (RM1549)
8. Lenovo Vibe Z2 Pro (RM1399)
9. ASUS Zenfone 2, 4GB RAM, 64GB storage (RM1399) or 128GB for Deluxe version(RM1599) .
10. Meizu MX4 Pro (RM1399)

At around RM1K, there is also Meizu MX4, 32GB (RM999)storage version.
Lesser known model would be the Lenovo Vibe X2 (RM799).

At super budget, ASUS Padfone S 16GB version and Lenovo Vibe Z now selling at RM599.

for me , go OP 1 cause i read op1 's ama reddit that they will released the marshmellow for OP 1 on the end of Nov

and other's i really out of idea and stay away for stupid Samsung and try hope for Sony or HTC IIMs

64GB not enough use meh ==

even my friend get 64GB also dunno how to put his ass of pain the games into his phone

erm if said original... u need to confirm with Satu Gadget, 7 Mobile, Direct D and some distro

but local[64GB Sandstone Blk] unit cost you 1270[1199+6% GST]

PS: Import unit dropped till ... 64GB RM 1049 [white/black]

tl:dr i get 16GB Bamboo model, which that time i bought from Dialog Hub.... and what i can said, storage for me is 0-worries cause i didn't used so much of apps at all and music and anime, yes haha , can 'piles' up to 4-5GB + 3Gb apps quite ok dy... why not

There is no guarantee which phone will get Marshmallow update, it is depend on manufacturer and developer, even getting Lollipop update is still in question in some region.
I can't answer for the custom rom support as well.

But, if you want your bet is save, I can tell is, the most popular phone, or flagship phone from big company will likely get Marshmallow update, (Samsung S5, Sony Z2, Honor 7, Oneplus One), but not guarantee every region will get it.

Phone from Xiaomi, Meizu, ASUS, Lenovo, will be half chance to get updated to Marshmallow, if they are already released one year ago, then the chances of update is getting less and less. They will focus on new device to getting the Marshmallow, and slowly push out update to older device, but no guarantee they will get it.

Of course, the same thing happen on custom rom too, most popular phone will get much wider and faster developer support, as oppose to those that is not popular.

One last thing, even your phone is not updated to Marshmallow, your phone will still doing fine for years.
I have a two year old phone, that just running on Android Jelly bean 4.2.2. and I can install anything on it without having any issue.
Even at some point, I do find out Google Play blocking me to install some apps, where I was mention my device is not compatible, I still can search for APK for the apps, and install to that phone anyway, and running without any issue.

In term of speed, that phone is not slow either. Having a SD 800 processor, it simply excel in speed, and can run any high end game smoothly that I install.

i looking some phone any brand to replace my oneplus one but must have better display lcd,  better rear camera and also better front to selfie than my opo..

budget around rm1500 or below is good..

if can, got also custom rom to mod..
actually i happy using my opo, just because front camera not very satify only..

any suggestion, thanks..