index build faster on 8G laptop than 30G server

I've been running an index build for almost an hour on my 30G server
that takes ~ 20 mins on my puny old macbook.

It seems like I've tuned all I can.. what am I missing?

Thanks,
Bill

Records to index: 33305041

--- Server:

  PostgreSQL 9.2.15 on x86_64-redhat-linux-gnu, compiled by gcc (GCC)
4.8.3 20140
911 (Red Hat 4.8.3-9), 64-bit

shared_buffers = 8GB            # min 128kB
temp_buffers = 2GB            # min 800kB
work_mem = 8GB                # min 64kB
checkpoint_segments = 256        # in logfile segments, min 1, 16MB each
seq_page_cost = 1.0            # measured on an arbitrary scale
random_page_cost = 1.0            # same scale as above
effective_cache_size = 20GB

   PID   USER        PR  NI  VIRT    RES  SHR S %CPU %MEM    TIME+ COMMAND
  4069 ec2-user  20   0 8596m 1.7g 1.7g R 99.8  5.6  67:48.36 postgres

Macbook:
  PostgreSQL 9.4.4 on x86_64-apple-darwin14.3.0, compiled by Apple LLVM
version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn), 64-bit

shared_buffers = 2048MB            # min 128kB
temp_buffers = 32MB            # min 800kB
work_mem = 8MB                # min 64kB
dynamic_shared_memory_type = posix    # the default is the first option
checkpoint_segments = 32        # in logfile segments, min 1, 16MB each

PID    COMMAND      %CPU TIME     #TH   #WQ  #PORTS MEM    PURG CMPRS  PGRP
52883  postgres     91.0 02:16:14 1/1   0    7      1427M+ 0B 622M-  52883